1. Field of the Invention
The present invention relates to a two-position pushbutton switch suitable for use in a digital camera.
2. Description of the Related Art
A conventional two-position pushbutton switch will be described below with reference to FIGS. 32 to 35. First, second, and third switch sections S3, S4, and S5 are held in a casing 51.
The first switch section S3 is formed of a membrane switch in which an insulating sheet 54 with an opening is interposed in a folded sheet 53 having a fixed contact and a movable contact, as shown in FIG. 34.
The second switch section S4 is formed of a membrane switch in which a fixed contact formed on a sheet 52 and a movable contact formed on a sheet 53 are opposed to each other via the opening of the sheet 54.
In the casing 51, a platelike support member 55 is also placed, and an operating member 56 is mounted on the support member 55.
The operating member 56 includes a mounting portion 56a mounted on the support member 55, an elastic portion 56b connected to the mounting portion 56a, a projection 56c formed at one end of the elastic portion 56b, an operating portion 56e connected to the mounting portion 56a via hinge portions 56d, a projection 56f formed at the end of the operating portion 56e, and a projection 56g formed at the bottom center of the operating portion 56e. 
The sheet 53 is bent in the shape of the letter U, and the first switch section S3 at the leading end thereof is placed on the upper surface of the operating portion 56e. A dome-shaped click spring 57 having a small working force and a small diameter is laid on the first switch section S3.
The second switch section S4, composed of three stacked sheets 52, 53, and 54, is placed on the upper surface of the support member 55, and a dome-shaped click spring. 58 having a great working force and a large diameter is laid on the second switch section S4 and below the projection 56g. The third switch section S5 is placed below the projection 56f. 
A key top 59 includes an operating portion 59a, two projections 59b and 59c formed on the lower side of the operating portion 59a, a support portion 59d formed at one end of the operating portion 59a, and a retaining portion 59e formed at the other end of the operating portion 59a. The key top 59 is supported in a cantilevered manner at the support portion 59d. 
When the key top 59 is mounted, the operating portion 59a is exposed from an opening portion 51a of the casing 51, the projection 59b is in contact with the projection 56c of the operating member 56, and the projection 59c is in contact with the click spring 57. Furthermore, the retaining portion 59e is retained on the inner surface of the casing 51 by the resilient force of the elastic portion 56b of the operating member 56.
The operation of the conventional two-position pushbutton switch will now be described. First, when the operating portion 59a of the key top 59 is pressed, the key top 59 tilts relative to the support portion 59d so as to simultaneously push the projection 56c and the click spring 57.
Then, the click spring 57 with a small working force is first inverted and presses the sheet 53 (folded portion) so that the movable contact is put into contact with the fixed contact thereon, thereby turning on the first switch section S3.
In this case, the relationship between the stroke A and the working force B of the key top 59 is represented by a curve C3, and the stroke A3 is short, as shown in FIG. 35.
When the key top 59 is further pressed in this state, the operating portion 56e of the operating member 56 is tilted via the hinge portions 56d, and therefore, the projection 56g of the operating portion 56e presses the click spring 58.
Subsequently, the click spring 58 with a large working force is inverted and presses the sheet 53 so that the movable contact is put into contact with the fixed contact of the sheet 52, thereby turning on the second switch section S4.
In this case, the stroke A and the working force B of the key top 59 have a relationship represented by a curve C4, as shown in FIG. 35.
In response to the tilting of the operating portion 56e, the projection 56f operates the third switch section S5 so as to switch from the ON state to an OFF state.
When the key top 59 is then released from pressing, it is pushed back by the elastic portion 56b, and the operating portion 56e is returned to its initial state by-the hinge portions 56d. Furthermore, the click springs 57 and 58 are inverted into their initial states because of their own resilient forces. This turns off the first and second switch sections S3 and S4, and returns the third switch section S5 into an ON state.
In a case in which such a two-position pushbutton switch is adopted-in a digital camera, focusing is performed by operating the first switch section S3 by a first press, and a shutter is released. by operating the second switch section S4 by a second press.
In the conventional two-state pushbutton switch, however, since the click spring 57 is pressed and inverted immediately after the key top 59 abuts the click spring 57, a stroke A3 of the first press is short, as shown in FIG. 35.
For this reason, when such a two-position pushbutton switch is adopted in a digital camera, the press stroke for focusing is short and the focusing operation is difficult. This decreases ease of use.
Furthermore, the operating member 56 includes the, mounting portion 56a and the operating portion 56e supported on the mounting portion 56a via the hinge portions 56d, and the operating 56e is able to move via the hinge portions 56d. This requires a large space in the lateral direction and increases the size of the switch.
Accordingly, an object of the present invention is to provide a two-position pushbutton switch in which operability is improved by extending the stroke of a key top for switching between switch sections.
Another object of the present invention is to provide a compact two-position pushbutton switch which allows smooth operation.
In order to overcome the above problems, according to an aspect of the present invention, there is provided a two-position pushbutton switch including: a first click spring to be inverted by a first working force; a first switch section to be operated by the inversion of the first click spring; a driving member disposed opposed to the first click spring so as to press the first click spring; a second switch section laid on the driving member; a second click spring to be inverted by a second working force, different from the first working force, so as to operate the second switch section; and a key top for pressing the second click spring, wherein a cushioning member is placed on at least one of the first and second click springs and the click spring is pressed via the cushioning member.
This can make a first press stroke long. For this reason, in a case in which such a two-position pushbutton switch is adopted in a digital camera, a press stroke for focusing can be made long, and the focusing operation is easy. This improves ease of use of the pushbutton switch.
The cushioning member may be placed on the second click spring.
This can make the first press stroke long. Moreover, since the key top and the second click spring are not in direct contact with each other, even when the key top rattles, no sound is produced by the contact therebetween.
The cushioning member may be placed on the first click spring.
This can make the first press stroke long. The first press stroke can be further extended by using the cushioning member in combination with a cushioning member placed on the second click spring.
Preferably, the two-position pushbutton switch further includes a casing for holding the key top, an operating portion of the key top is exposed from an opening portion of the casing, and the key top is elastically pressed against the casing and supported therein by the cushioning,member.
In this case, the cushioning member also serves to press the key top and to thereby prevent the key top from rattling. This also reduces the number of components and lowers the cost.
Preferably, the first working force for the first click spring is greater than the second working force for the second click spring.
In this case, after the second click spring at the upper position is inverted, the lower first click spring is inverted. The driving member can be stably supported by the lower click spring with a large working force.
Preferably, the diameter of the first click spring is smaller than that of the second click spring, and the thickness of the first click spring is greater than that of the second click spring.
This makes it possible to reliably make the working force for the first click spring greater than that for the second click spring and to thereby allow reliable operation.
Preferably, the first and second click springs are made of a metal leaf spring and also serve as movable contacts of the first and second switch sections.
This reduces the number of components, improves assembly efficiency, and lowers the cost.
Preferably, the two-position pushbutton switch further includes a flexible insulating substrate having fixed contacts for the first and second switch sections, and the flexible insulating substrate is bent in the shape of the letter S and is placed opposed to the first and second-click springs.
In this case, the fixed contacts can be formed in the same plane of the flexible insulating substrate, and therefore, productivity is increased.
Preferably, the two-position pushbutton switch further includes a support member for supporting the first switch section, the support member has a plurality of guide projections extending in the pressing direction of the key top, and the driving member is slid along the guide projections in the pressing direction.
This makes it possible to reduce the space for supporting the driving member and to thereby reduce the size, and to make the sliding motion of the driving member smooth.
According to another aspect of the present invention, there is provided a two-position pushbutton switch including: a first click spring to be inverted by a first working force; a first switch section to be operated by the inversion of the first click spring; a driving member placed opposed to the first click spring so as to press the first click spring; a second switch section placed on the driving member; a second click spring to be inverted by a second working force, different from the first working force, so as to operate the second switch section; a key top for pressing, the second click spring; and a guide member for guiding the motion of the driving member, wherein the driving member is slid along the guide member in the pressing direction of the key top.
Since the space for holding the driving member can be reduced, the size of the two-position pushbutton switch can also be reduced. Moreover, since the driving member can be moved stably, operability is enhanced.
Preferably, the guide member includes a plurality of guide projections arranged to surround the second switch section, and a support member is further provided so as to support the first switch section.
This reduces the size of the pushbutton switch and allows the driving member to be moved stably.
Preferably, the guide projections are shaped like a bendable column, and hook portions are formed at the leading ends of the guide projections so as to retain the driving member.
In this case, the driving member can be easily assembled and the position thereof can be regulated reliably.
The guide member may have a connecting portion for connecting the guide projections.
This facilitates assembly of the guide member and improves productivity.
Preferably, the first switch section is placed on a flexible insulating substrate, a projection is formed at the bottom of the connecting portion of the guide member, the guide member is mounted on the support member by the projection, and the flexible insulating substrate laid on the support member is sandwiched between the support member and the connecting portion.
In this case, the guide member and the flexible insulating substrate can be mounted simultaneously. This increases productivity and prevents the first switch section from lifting.
Preferably, the driving member has a flat portion for holding the second switch section thereon, and the flat portion has a plurality of guide portions to be guided by the guide projections.
This allows the driving member to be moved stably and smoothly.
Preferably, fixed contacts of the first and second switch sections are formed-on the same flexible insulating substrate, and the flexible insulating substrate is placed in a form bent in the shape of the letter S.
Since the fixed contacts can be formed on the same plane of the flexible insulating substrate, productivity is increased.
Preferably, the driving member has a pair of projecting latch portions, the flexible insulating substrate has a pair of holes, and the second switch section is held on the driving member by latching the latch portions in the holes.
In this case, the position of the second switch section with respect to the driving member can be reliably ensured, and the second switch section can be mounted without lifting.
Preferably, the first and second click springs are made of a metal leaf spring, and also function as movable contacts of the first and second switch sections.
This reduces the number of components, improves assembly efficiency, and lowers the cost.
Further objects. features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference-to the attached drawings.